1. Field of the Invention
This invention relates to an apparatus for determining the polarity of bonding points.
2. Prior Art
As a method to detect connection faults in wire bonding after the wire is connected to a first bonding point, Japanese Patent Application Publication No. 1-58868, for example, is known. In this prior art, when detecting the connection fault of the first bonding point, it is necessary to apply positive or negative voltage to the first bonding point, switching from one to the other, depending on the polarity of the first bonding point.
FIGS. 3(a) through 3(d) show the polarities of the first bonding point. In these Figures, reference numeral 1 represents a lead frame, 2 a chip bonded to the lead frame 1, and 3 a wire connected to an electrode (which is the first bonding point) of the chip 2. As shown in these Figures, there are various electrodes (first bonding points) which are different in polarities. Therefore, when detecting connection faults at the first bonding points, it is necessary to apply positive or negative voltage, switching from one to the other depending on the polarity.
FIG. 3(a) shows that the first bonding point sends the current forward (hereinafter referred to as having "positive polarity"), and detection is performed by applying positive voltage. In FIG. 3(b), the first bonding point sends the current backward (hereinafter referred to as having "negative polarity"); as a result, detection is performed by applying negative voltage.
In FIG. 3(c), the portion of the chip 2 corresponding to the first bonding point is of a non-conductive material (hereinafter referred to as having "polarity with no detection required"). Accordingly, no detection is possible regardless of whether a positive or negative voltage is applied, and therefore detection is not needed. In FIG. 3(d), a portion of the chip 2 that corresponds to the first bonding point has no polarity but has some resistance (hereinafter referred to having "no polarity"); accordingly, detection can be performed by applying either positive or negative voltage.
As described above, when detecting connection faults at the first bonding point, it is necessary to change the applied voltage depending on the polarity of the first bonding point. Accordingly, it is also necessary that the polarity of the first bonding point be checked beforehand so as to apply voltage that is suitable for such a checked first bonding point.
Currently, the determination of the polarity of the first bonding point is performed by an operator. The operator moves a probe so that it touches each bonding point to determine their polarities by applying positive and negative voltages and monitoring the polarity of the bonding point on a display.
In this conventional way, since an operator determines the polarity of each bonding point, it requires a great amount of time and effort, and it also involves the risk of error determinations.